Two adjacent epiblast cells of the inner cell mass (embryoblast)

High power TEM of the same area of the stage 3 embryo in vitro shown in Figure 21 showing two adjacent epiblast cells of the inner cell mass (embryoblast), 145-170 hours post-insemination (original magnification x 10,800). Clumps of heterochromatin are attached to the inner nuclear membrane and scattered in the nucleoplasm. Polyribosomes and free ribosomes are abundant in the cytoplasm. The mitochondria are elongated or curved and contain transversely running cristae. Lengths of rough endoplasmic reticulum are closely associated with the mitochondrial surfaces. Bundles of microfilaments are present in the cytoplasm.